Still looking into what I consider a slow stick circuit in an old excavator as well as a difficult to control down control on the stick. I am trying to confirm the difference between the relief and load check. From what I gather from the manuals, my system operates at 3600 psi. The relief valve for each circuit is set at 3600 and the load check is set at 4000 so theoretically the load check should never open unless the relief valve malfunctions? make up valve - from what I gather, this is a short circuit valve allowing the transfer directly of oil from one side of a cylinder to the other. Because I am fighting a stick that I cannot inch down (6" jump minimum"), indication is the spring on the make up might be lazy? I realize the spool might be hanging up or something but not real sure if there really is a way to test this function because the pressure in the cylinder would not be using pump pressure until the makeup closes again. Also, because there seems to be a glitch at the bottom where the make up would close pump pressure should kick in crowd the stick, I kinda of think the make up is not closing back up correctly. Do I have this right?
The line relief valve (what you refer to as the load check) is designed to relieve pressure in a single cylinder (or single circuit) if that circuit becomes overloaded, even if the control valve for the circuit is in the neutral position thus "blocking" the flow of oil back to the tank. It's topo stop hoses bursting.
does the cylinder creep and/or become very hot during operation? it might it bypassing internally, tell tale sign will be the cylinder might be slow, jerky and have some creep as well as getting much hotter than normal you can test this by dead ending the ram and removing the oposing hyd line and stalling out the hydraulics to see if any oil comes out the ram
No heat has been detected on the cylinder and there is no creep, it will stay in position with the engine off all day. Nige, the main valve has 6 valve ports per spool. 1 makeup per side of a spool, 1 relief valve per side of spool, and one centrally located load check. I am still a little confused here.
The make up valve, often called anti cav valves, are there to allow oil to flow quickly from one side of cylinder to the other if it moves too quick, for these to work good they need a little back pressure in the system. If an anti cav valve is leaking you will have cylinder creep. There should be 2 reliefs.. Main and secondary. Mains is lower, like 320 Bar, and secondaries are set around 360-380. Mains are what set your operating pressure, and the secondaries are an overload protection. I think what you're calling the make up is actually the load check.. The load check closes when you let go of a lever and there is pressure in the circuit.(like if you had a full bucket and boom all the way up). If the load check was not there, or faulty, then the boom would drop a bit until the pump outlet pressure was enough to lift the boom. This may be the problem in your case. The load checks are easy to check. They usually just look like a plug, behind that there should be a spring and small spool. Just make sure you have the attachment on the ground and no pressure in the system!!! Hope this helps.
thanks. I think we are getting somewhere. Per a couple explanations, I think I do better understand that the makeup is only there to allow short circuit fluid flow if the spool is neutral and there is an overload force put on the cylinder. Regarding the load check, I thought those were individual pressure checks allowed to open when a cylinder was maxed out thus limiting the pressure but as I better understand the "check" is really a check valve keeping the pressure already at the cylinder constant until pressure behind it is greater thus the cylinder cannot actually drop before moving as desired. Because I have no creep issues at all or strange dropping issues, I think we can nearly write off the valves now. What I am fighting is "inching" the stick down. try as I might, about 6" is the best I can do with everything at full extension. I just do not know what is worn that is causing this. Obviously this might be considered a non-issue to some. My primary issue is the slow stick response. Book indicates that with pump crossovers off (1 pump for stick), stick should fully extend in 4sec. I am probably 10-15sec. If I hit the crossover pedal for dual pump operation, it gets MUCH faster but should then extend in 2.4sec which is off mark. All thinks considered, it seems there is an issue with one pump circuit which what I read so far could be a pump, summing valve, combining valve, or just a relief valve hung up. I have a hard time so far believing the pump is actually this messed up since it is not making any noise. The only other thing it runs is one of the tracks and I am working on those right now so no drive. I am trying to figure out a way to troubleshoot this issue.
I would also mention that though I plan to check the pilot pressures as well as main pump pressures, it is hard to believe the pump signal pressure would be out of whack since those pressure lines are in parallel. There is actually 2 small lines on the pumps and not sure which is which yet but I know one should get signal pressure from the underspeed valve to destroke or reduce volume in a lug condition. They both get the same pressure and the other pump seems to do fine.
If there are 2 pumps that feed the stick circuit, try them one at a time and check cycle time to extend/retract, if both pumps are the same time then they are good. If you disconnect those 2 lines off one pump and cap them off, that should isolate that pump. When you say you're working on the tracks, are the finals still on and hooked up? If so you could jack up one side at a time and time the revolutions, the more revolutions you time the more accurate it will be. E.G mark a spot on sprocket and check how long it takes to do 20 revolutions. Do you have test gauges? you could put a tee fitting on the servo line at the control valve spool for stick function, then you can check the pressure that is moving the spool. The pressure should slowly rise as you move the lever, and be proportional to lever stroke. So if you move lever a little, there should only be a little amount of pressure operating spool.
Track was tested and LH is half the speed of the RH track. I have isolated stick operation on just the one pump and it is slow. I think we are down to the pump stroke servo valve or the pump itself.